Process of producing calcium molybdate



Patented Aug. 23, 1932 UNITE 5T PAT E nnnsr roKonnr, or LEIPZIG, GERMANY, Ass snon To is. rnniannr'nnusrn n GERMANY PROCESS OF PRODUCING CALCIUM No Drawing. Application filed October 11, 1929, SerialQNo. 339,104, and; in Germany December 8 x This invention relates to the production of molybdates of calcium.

In iron and steel industries calcium molybdate is at present being employed, to a continuously increasing extent, for producing ferromolybdenum and molybdenum steel. This calcium molybdate was hitherto usually made by starting from roasted molybdenite, preparing an alkali metal molyb-date solution and precipitating therefrom calcium molybdate by adding milk of lime or a calcium salt under suitable conditions.

For simplifying this two-step process it has also been proposed, to boil raw molybdic acid with milk of lime and to evaporate the resulting product to dryness. From the fact that evaporation is expressly called for as an essential step of this process it appears that milk of lime was employed in excess this giving rise to the formation of soluble molybdates. As a rather considerable amount of liquid is neededfor the reaction, this evaporation is a grave encumbrance on the process in questionand would surely have i been avoided had conditions been known for in any other way avo1d1ng the losses caused by the formation of soluble molybdates. Consequently this rocess has commercially failed up to date, the possibility of carrying out the process in one operation being too heavily paid for by the necessity of evaporating the resulting product to dryness.

Now I have found that by maintaining certain conditions of working it is possible to avoid the formation of water-soluble calcium molybdate and therefore also the step of evaporation, thus rendering the one-step process commercially feasible. By treating the roasted molybdenite with milk of lime, preferably at boiling temperature, in such a manner as to avoid any excess of lime being present in the solution, the insoluble molybdate precipitates directly without any formation of soluble molybdates. This is obtained by carrying out the reaction in a solution in which the concentration of the cal cium hydroxide is continuously kept at a level which is represented by a just merely testable alkaline reaction.

It is Well known that molybdic acid is soluble inwater, though onlyto a slight but perceptible extent. According to my inven-f tion the reaction with'the gradually added milk of lime takes place in such "a way that the dissolved molybdic "acid enters at once into'reactio-n with the milk of'lime so as to form insoluble calcium, molybdate-whereby the small amounts of moly'bdic' acid thus withdrawn, are immediately -replaced by furher quantities entering into the solution which, in their turn, are reacted uponby the milk'of -lime addedin the'ineantimeQetcJ As already mentioned above, an excess of lime should be carefully avoided tofprevent the formation of soluble molybdates. This is preferably attained by continuouslytest ing the basicity of the solution by means of litmus-paper, care being taken thatthe basicity never exceedsthe amount -require.d for-"' iu'st slightly blueing red litmus paper.

'Of course, when following my new math-" od, the contaminations or accompanying'eom stituents contained in the roasted *inateria l,= above all the gangueof the ore, remaini-nthe productr However, as*far as-ores of commercial purity are concerned, 'tliis'is lof no censequence regarding the purposes in ques-f tion. The acid gangue moreover renders the addition ofsand su-perfiuouswhich otherwise is required for thesmel'ting processs. ;Tl;1egreat-er part ofthe' arsen c contents as [already eliminated by the roasting operation if? the latter be suitably conducted; Anyconsid erable contents of copperor bismuth may-be removed, before roasting", according; to "any of the well known methods.

The following exampleis adapted to illns';

trate my invention, but it ,isnot'intendedqto.

limit it thereto.

The product obtained about50% of molybdenum), is levigatedin y a thorough a v:9o1-"5; mg of molybdenlte thejcomenhiated m I in which it is usually marketed (containing added to the boiling molybdenitesuspension,

care being taken, that the milk offlinie is" addedv only in such small quantities that'a weakly alkaline reaction of the solution is attained. The reaction is tested by means of litmus paper. If the alkaline reaction of the solution, even after three minutes of uninterrupted boiling and stirring is still 5 maintained, formation of they calcium molybdate is completed. Any excess of milk of lime should be avoided in order to preventparts of the calcium molybdate from redis solvingl However, if the alkaline reaction of the solution is not permanent, the formation of the calcium molybdate is still unac complished. b

Upon completion of" the conversion, the reaction product is washed by decanting andsubsequently filtered and dried. The product thus obtained from molybdenite in the concentrated form contains approximately 40% molybdenum, and may be introduced I into vthe steel bath in either a loose state or in the-form of briquettes produced therefrom. In view of. the lgangue still present in the final product according to the above described process, the briquettes formed therefromare more solid than those made I 26 from pure calcium molybdateh The production of calcium molybda'te according to the present invention requiresso few technical appliances that the conversion may be effected at thesite of production of 80 the ores thereby obtaining a product of increased value with little additional expense.

I claim: V Y 1 v1. The a process which comprises gradually adding calcium hydroxide to a substance containing molybdenum oxide in thepresence of water. at such a rate as to maintain, in the solution, a basicity just suflicient to blue litmus paper, and removing the precipitate.

v40 J t2. iThe process which comprises gradually 7 adding milk of lime to a substance containing molybdenum oxide'in the presence of 7 water at. such a rate as to maintain, in the, solution, a basi'city just sufiicient to blue lit- "mus paper, and removing the precipitate.

The process which comprises gradually adding milk of lime to roasted molybdeniteinthe presence of water at such a rate asto maintain, in the solution, a basicity just 6.0 sufficient to blue litmus paper, and removing the precipitate. I I V v, 4. The process which comprises gradually adding milk of lime to a suspension of finely divided roasted molybdenite in water at such a rate as to maintain, in the solution a basicity just suflicient to blue litmus paper, and

removing the precipitate.

5. The process which comprises gradually adding milk of lime to a suspension of finely divided roasted molybdenite in boiling water at such a rate as to maintain, in the solug tion, a basicity just sufiici-ent to blue litmus paper, and removing the precipitate.

testimony whereof, I aflix mv'signature.

' 6: I ERNST PO'KOBNY, 

